Advanced receive channel architecture

ABSTRACT

This relates to an architecture of a receive channel circuit used during both a spectrum analysis phase and a touch panel detection phase. Various components of the receive channel can be used during both the spectrum analysis phase and the touch panel detection phase. For example, a plurality of digital signal mixers used in the receive channel circuit can be used to demodulate signals during both a spectrum analysis phase and a touch sensor panel detection phase. In addition, the number of digital mixers needed in the receive channel can be reduced by dividing groups of signals to be demodulated into multiple sets of signals and demodulating each set at different times.

FIELD OF THE INVENTION

This relates to touch sensor panels used as input devices for computingsystems, and more particularly, to demodulating signals received from atouch sensor panel.

BACKGROUND OF THE INVENTION

Many types of input devices are presently available for performingoperations in a computing system, such as buttons or keys, mice,trackballs, touch sensor panels, joysticks, touch screens and the like.Touch screens, in particular, are becoming increasingly popular becauseof their ease and versatility of operation as well as their decliningprice. Touch screens can include a touch sensor panel, which can be aclear panel with a touch-sensitive surface, and a display device thatcan be positioned behind the panel so that the touch-sensitive surfacecan substantially cover the viewable area of the display device. Touchscreens can allow a user to perform various functions by touching thetouch sensor panel using a finger, stylus or other object at a locationdictated by a user interface (UI) being displayed by the display device.In general, touch screens can recognize a touch event and the positionof the touch event on the touch sensor panel, and the computing systemcan then interpret the touch event in accordance with the displayappearing at the time of the touch event, and thereafter can perform oneor more actions based on the touch event.

Touch sensor panels can be formed from a matrix of drive and senselines, with sensors or pixels present where the drive and sense linescross over each other while being separated by a dielectric material inmulti-layer embodiments, or where the drive and sense lines are adjacentto each other in single-sided embodiments. Each drive line can be drivenby a stimulation signal, and touch locations can be identified becausethe charge injected into the sense lines due to the stimulation signalis proportional to the amount of touch. However, the high voltage thatcan be required for the stimulation signal can force the sensor panelcircuitry to be larger in size, and separated into two or more discretechips. In addition, touch screens formed from capacitance-based touchsensor panels and display devices such as liquid crystal displays (LCDs)can suffer from noise problems because the voltage switching required tooperate an LCD can capacitively couple onto the sense lines of the touchsensor panel and cause inaccurate measurements of touch. Furthermore,alternating current (AC) adapters used to power or charge the system canalso couple noise into the touchscreen. Other sources of noise caninclude switching power supplies in the system, backlight inverters, andlight emitting diode (LED) pulse drivers. Each of these noise sourceshas a unique frequency and amplitude of interference that can changewith respect to time. Accounting for noise problems can requireadditional logic circuitry, which can use up more die space and power.

SUMMARY OF THE INVENTION

Various embodiments of the present invention can use particularcomponents of a receive channel circuit during both a spectrum analysisphase and a touch panel detection phase of a touch sensor panel. Aspectrum analysis phase can include analyzing noise to identify lownoise stimulation frequencies. A touch panel detection phase can includeusing one or more stimulation frequencies and phases to detect andlocalize touch events on the touch sensor panel.

When performing a spectrum analysis, no stimulation signal is applied toany of the drive lines in the touch sensor panel. The sum of the outputof all receive channels, which can represent the total charge beingapplied to the touch sensor panel including all detected noise, can bedemodulated using in-phase (I) and quadrature (Q) signals of one or morefrequencies. The demodulated outputs can be used to calculate themagnitude of the noise at that particular frequency, wherein the lowerthe magnitude, the lower the noise at that frequency. One or more lownoise frequencies can be selected for use in a subsequent touch sensorpanel scan.

When performing the touch sensor panel scan function, one or moreselected low noise frequencies can be used to simultaneously stimulatethe drive lines of the touch sensor panel, and signals received from thesense lines connected to the receive channels can be demodulated usingthe selected low noise frequencies. The demodulated signals can then besaved. After all steps have been completed, the saved results can beused in calculations to determine an image of touch for the touch sensorpanel at each frequency.

The number of digital signal mixers used in the receive channel circuitcan be reduced by using the same digital signal mixers to performfunctions during both a spectrum analysis phase and a touch paneldetection phase. For example, the same digital mixers can be used todemodulate signals during both a spectrum analysis phase and a touchsensor panel detection phase. Moreover, groups of signals beingdemodulated using the signal mixers can be divided into multiple sets ofsignals and each set can be demodulated at different times. Doing so canfurther reduce the number of mixers needed to perform the demodulationfunctions. As an example, if the signals to be demodulated are dividedinto two sets, then the number of signal mixers need to demodulate thesignals can be reduced by half.

Furthermore, the size of a sine look-up table (LUT) for a numericallycontrolled oscillator can be reduced by taking advantage of the symmetryof the sine waveform. For example, a quarter of a sine waveform can besaved in the LUT and the remaining quadrants of the waveform can bederived based on the symmetry of the sine wave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary computing system that can utilizemultiple digital mixers to perform spectrum analysis of noise andidentify low noise stimulation frequencies, and can utilize multiplestimulation frequencies and phases to detect and localize touch eventson a touch sensor panel according to various embodiments of thisinvention.

FIG. 2 a illustrates an exemplary mutual capacitance touch sensor panelaccording to various embodiments of this invention.

FIG. 2 b is a side view of an exemplary pixel in a steady-state(no-touch) condition according to various embodiments of this invention.

FIG. 2 c is a side view of an exemplary pixel in a dynamic (touch)condition according to various embodiments of this invention.

FIG. 3 illustrates an exemplary receive channel or event detection anddemodulation circuit according to various embodiments of this invention.

FIG. 4 a illustrates a simplified block diagram of an exemplary Nchannel receive circuit (also referred to as “receive channel circuit”)according to various embodiments of this invention.

FIG. 4 b illustrates a sine look-up table (LUT) used to provide adigital values for an NCO to construct a sine waveforms in accordancewith various embodiments of this invention.

FIG. 5 a illustrates an exemplary timing diagram showing an LCD phaseand touch sensor panel phase according to various embodiments of thisinvention.

FIG. 5 b illustrates an exemplary flow diagram describing an LCD phaseand the touch sensor panel phase in accordance with various embodimentsof this invention.

FIG. 6 a illustrates an exemplary mobile telephone that can utilize areceive channel circuit to perform both spectrum analysis functions andtouch panel scan functions according to various embodiments of thisinvention.

FIG. 6 b illustrates an exemplary digital audio player that can utilizea receive channel circuit to perform both spectrum analysis functionsand touch panel scan functions according to various embodiments of thisinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of preferred embodiments, reference is madeto the accompanying drawings which form a part hereof, and in which itis shown by way of illustration specific embodiments in which theinvention can be practiced. It is to be understood that otherembodiments can be used and structural changes can be made withoutdeparting from the scope of the embodiments of this invention.

This relates to the use of particular components of a receive channelcircuit during both a spectrum analysis phase and a touch paneldetection phase. A spectrum analysis phase can include analyzing noiseto identify low noise stimulation frequencies. A touch panel detectionphase can include using one or more stimulation frequencies and phasesto detect and localize touch events on a touch sensor panel.

When performing a spectrum analysis, no stimulation signal is applied toany of the drive lines in the touch sensor panel. The sum of the outputof all receive channels, which can represent the total charge beingapplied to the touch sensor panel including all detected noise, can bedemodulated using in-phase (I) and quadrature (Q) signals of one or morefrequencies. The demodulated outputs can be used to calculate themagnitude of the noise at that particular frequency, wherein the lowerthe magnitude, the lower the noise at that frequency. One or more lownoise frequencies can be selected for use in a subsequent touch sensorpanel scan.

When performing the touch sensor panel scan function, one or moreselected low noise frequencies can be used to simultaneously stimulatethe drive lines of the touch sensor panel, and signals received from thesense lines connected to the receive channels can be demodulated usingthe selected low noise frequencies. The demodulated signals can then besaved. After all steps have been completed, the saved results can beused in calculations to determine an image of touch for the touch sensorpanel at each frequency.

In accordance with various embodiments, the number of digital signalmixers used in the receive channel circuit can be reduced by using thesame digital signal mixers to perform functions during both a spectrumanalysis phase and a touch panel detection phase. For example, the samedigital mixers can be used to demodulate signals during both a spectrumanalysis phase and a touch sensor panel detection phase. Moreover,groups of signals being demodulated using the signal mixers can bedivided into multiple sets of signals and each set can be demodulated atdifferent times. Doing so can further reduce the number of mixers neededto perform the demodulation functions. As an example, if the signals tobe demodulated are divided into two sets, then the number of signalmixers need to demodulate the signals can be reduced by half.

Furthermore, in accordance with various embodiments, the size of a sinelook-up table (LUT) for a numerically controlled oscillator can bereduced by taking advantage of the symmetry of the sine waveform. Forexample, a quarter of a sine waveform can be saved in the LUT and theremaining quadrants of the waveform can be derived based on the symmetryof the sine wave.

Although some embodiments of this invention may be described herein interms of mutual capacitance touch sensors, it should be understood thatembodiments of this invention are not so limited, but are generallyapplicable to other types of touch sensors such as self capacitancetouch sensors. Furthermore, although the touch sensors in the touchsensor panel may be described herein in terms of an orthogonal array ofdrive lines and sense lines, it should be understood that embodiments ofthis invention are not limited to orthogonal arrays, but can begenerally applicable to touch sensors arranged in any number ofdimensions and orientations, including diagonal, concentric circle, andthree-dimensional and random orientations. In addition, the touch sensorpanel described herein can be either a single-touch or a multi-touchsensor panel, the latter of which is described in Applicant's co-pendingU.S. application Ser. No. 10/842,862 entitled “Multipoint Touchscreen,”filed on May 6, 2004 and published as U.S. Published Application No.2006/0097991 on May 11, 2006, the contents of which are incorporated byreference herein in their entirety for all purposes.

FIG. 1 illustrates exemplary computing system 100 that can performspectrum analysis of noise and identify low noise stimulationfrequencies, and can utilize multiple stimulation frequencies and phasesto detect and localize touch events on a touch sensor panel according toembodiments of the invention. Computing system 100 can include one ormore panel processors 102 and peripherals 104, and panel subsystem 106.One or more panel processors 102 can include, for example, ARM968processors or other processors with similar functionality andcapabilities. However, in other embodiments, the panel processorfunctionality can be implemented instead by dedicated logic, such as astate machine. Peripherals 104 can include, but are not limited to,random access memory (RAM) or other types of memory or storage, watchdogtimers and the like. Panel subsystem 106 can include, but is not limitedto, one or more receive channels 108, channel scan logic 110 and driverlogic 114. Channel scan logic 110 can access RAM 112, autonomously readdata from the receive channels and provide control for the receivechannels. In addition, channel scan logic 110 can control driver logic114 to generate stimulation signals 116 at various frequencies andphases that can be selectively applied to drive lines of touch sensorpanel 124. In some embodiments, panel subsystem 106, panel processor 102and peripherals 104 can be integrated into a single application specificintegrated circuit (ASIC).

Touch sensor panel 124 can include a capacitive sensing medium having aplurality of row traces or driving lines and a plurality of columntraces or sensing lines, although other sensing media can also be used.The drive and sense traces can be formed from a transparent conductivemedium such as Indium Tin Oxide (ITO) or Antimony Tin Oxide (ATO),although other transparent and non-transparent materials such as coppercan also be used. In some embodiments, the drive lines and sense linescan be perpendicular to each other, although in other embodiments othernon-Cartesian orientations are possible. For example, in a polarcoordinate system, the sensing lines can be concentric circles and thedriving lines can be radially extending lines (or vice versa). It shouldbe understood, therefore, that the terms “row” and “column,” “firstdimension” and “second dimension,” or “first axis” and “second axis” asused herein are intended to encompass not only orthogonal grids, but theintersecting traces of other geometric configurations having first andsecond dimensions (e.g. the concentric and radial lines of apolar-coordinate arrangement). The drive lines and sense lines can beformed on a single side of a substantially transparent substrateseparated by a substantially transparent dielectric material, onopposite sides of the substrate, or on two separate substrates separatedby the dielectric material.

In some two-layer touch sensor panel embodiments, at the “intersections”of the traces, where the traces pass above and below (cross) each other(but do not make direct electrical contact with each other), the tracescan essentially form two electrodes (although more than two traces couldintersect as well). Each intersection of row trace and column trace canrepresent a capacitive sensing node and can be viewed as picture element(pixel) 126, which can be particularly useful when touch sensor panel124 is viewed as capturing an “image” of touch. (In other words, afterpanel subsystem 106 has determined whether a touch event has beendetected at each touch sensor in the touch sensor panel, the pattern oftouch sensors in the multi-touch panel at which a touch event occurredcan be viewed as an “image” of touch (e.g. a pattern of fingers touchingthe panel).) The capacitance between row and column electrodes appearsas a stray capacitance when the given row is held at direct current (DC)voltage levels and as a mutual signal capacitance Csig when the givenrow is stimulated with an alternating current (AC) signal. The presenceof a finger or other object near or on the touch sensor panel can bedetected by measuring changes to a signal charge Qsig present at thepixels being touched, which is a function of Csig. Each column of touchsensor panel 124 can drive receive channel 108 (also referred to hereinas an event detection and demodulation circuit) in panel subsystem 106.

Computing system 100 can also include host processor 128 for receivingoutputs from panel processor 102 and performing actions based on theoutputs that can include, but are not limited to, moving an object suchas a cursor or pointer, scrolling or panning, adjusting controlsettings, opening a file or document, viewing a menu, making aselection, executing instructions, operating a peripheral deviceconnected to the host device, answering a telephone call, placing atelephone call, terminating a telephone call, changing the volume oraudio settings, storing information related to telephone communicationssuch as addresses, frequently dialed numbers, received calls, missedcalls, logging onto a computer or a computer network, permittingauthorized individuals access to restricted areas of the computer orcomputer network, loading a user profile associated with a user'spreferred arrangement of the computer desktop, permitting access to webcontent, launching a particular program, encrypting or decoding amessage, and/or the like. Host processor 128 can also perform additionalfunctions that may not be related to panel processing, and can becoupled to program storage 132 and display device 130 such as an LCDdisplay for providing a UI to a user of the device.

In some systems, sensor panel 124 can be driven by high-voltage driverlogic. The high voltages that can be required by the high-voltage driverlogic (e.g. 18V) can force the high-voltage driver logic to be formedseparate from panel subsystem 106, which can operate at much lowerdigital logic voltage levels (e.g. 1.7 to 3.3V). However, in embodimentsof the invention, on-chip driver logic 114 can replace the off-chip highvoltage driver logic. Although panel subsystem 106 can have low, digitallogic level supply voltages, on-chip driver logic 114 can generate asupply voltage greater that the digital logic level supply voltages bycascoding two transistors together to form charge pump 115. Charge pump115 can be used to generate stimulation signals 116 (Vstim) that canhave amplitudes of about twice the digital logic level supply voltages(e.g. 3.4 to 6.6V). Although FIG. 1 shows charge pump 115 separate fromdriver logic 114, the charge pump can be part of the driver logic.

FIG. 2 a illustrates exemplary mutual capacitance touch sensor panel 200according to embodiments of the invention. FIG. 2 a indicates thepresence of a stray capacitance Cstray at each pixel 202 located at theintersection of a row 204 and a column 206 trace (although Cstray foronly one column is illustrated in FIG. 2 a for purposes of simplifyingthe figure). In the example of FIG. 2 a, AC stimuli Vstim 214, Vstim 215and Vstim 217 can be applied to several rows, while other rows can beconnected to DC. Vstim 214, Vstim 215 and Vstim 217 can be at differentfrequencies and phases, as will be explained later. Each stimulationsignal on a row can cause a charge Qsig=Csig×Vstim to be injected intothe columns through the mutual capacitance present at the affectedpixels. A change in the injected charge (Qsig_sense) can be detectedwhen a finger, palm or other object is present at one or more of theaffected pixels. Vstim signals 214, 215 and 217 can include one or morebursts of sine waves. Note that although FIG. 2 a illustrates rows 204and columns 206 as being substantially perpendicular, they need not beso aligned, as described above. As described above, each column 206 canbe connected to a receive channel (see receive channels 108 in FIG. 1).

FIG. 2 b is a side view of exemplary pixel 202 in a steady-state(no-touch) condition according to embodiments of the invention. In FIG.2 b, an electric field of electric field lines 208 of the mutualcapacitance between column 206 and row 204 traces or electrodesseparated by dielectric 210 is shown.

FIG. 2 c is a side view of exemplary pixel 202 in a dynamic (touch)condition. In FIG. 2 c, finger 212 has been placed near pixel 202.Finger 212 is a low-impedance object at signal frequencies, and has anAC capacitance Cfinger from the column trace 204 to the body. The bodyhas a self-capacitance to ground Cbody of about 200 pF, where Cbody ismuch larger than Cfinger. If finger 212 blocks some electric field lines208 between the row and column electrodes (those fringing fields thatexit the dielectric and pass through the air above the row electrode),those electric field lines are shunted to ground through the capacitancepath inherent in the finger and the body, and as a result, the steadystate signal capacitance Csig is reduced by ΔCsig. In other words, thecombined body and finger capacitance act to reduce Csig by an amountΔCsig (which can also be referred to herein as Csig_sense), and can actas a shunt or dynamic return path to ground, blocking some of theelectric fields as resulting in a reduced net signal capacitance. Thesignal capacitance at the pixel becomes Csig−ΔCsig, where Csigrepresents the static (no touch) component and ΔCsig represents thedynamic (touch) component. Note that Csig−ΔCsig may always be nonzerodue to the inability of a finger, palm or other object to block allelectric fields, especially those electric fields that remain entirelywithin the dielectric material. In addition, it should be understoodthat as a finger is pushed harder or more completely onto themulti-touch panel, the finger can tend to flatten, blocking more andmore of the electric fields, and thus ΔCsig can be variable andrepresentative of how completely the finger is pushing down on the panel(i.e. a range from “no-touch” to “full-touch”).

FIG. 3 illustrates exemplary receive channel 300 (also known as sensechannel or analog channel) in accordance with various embodiments. Oneor more receive channels 300 can be present in a multi-touch subsystem,such as multi-touch subsystem 106. Referring again to FIG. 3, one ormore sense lines 206 (FIG. 2 a) of a multi-touch panel can be coupableto each receive channel 300. Each receive channel 300 can include chargeamplifier 302, anti-aliasing filter 304 and analog-to-digital converter(ADC) 306, digital mixer 308 (e.g., multiplier circuit) and accumulator310. Digital mixer 308 can be driven by NCO (Numerically ControlledOscillator) 312 that may include amplitude window shaping using a windowfunction. Receive channel 300 can be driven by an input signal (e.g.,Vstim or a DC signal), resulting in a steady state signal capacitanceCsig when no finger, palm or object is present or a dynamic signalcapacitance Csig−ΔCsig when a finger, palm or other object is present.With further reference to FIG. 3, receive channel 300 can receive asignal representative of the capacitance or change in capacitance (Csigor Csig−ΔCsig) from a touch panel and convert it into the digitaldomain, demodulate the digital signal with a demodulation waveform andaccumulate the output in accumulator 310. The accumulated output canthen be stored in result register 314 and provided for furtherprocessing. In accordance with some embodiments, receive channel 300 canbe implemented as part of an ASIC.

FIG. 4 a illustrates a block diagram of exemplary N channel receivechannel circuit 400 (also referred to herein as “receive channelcircuit”) that can be configured both as a spectrum analyzer and astouch panel scan logic according to various embodiments. Receive channelcircuit 400 can be present in the panel subsystem 106 (FIG. 1). Incontrast to receive channel 300 of FIG. 3, which can receive signalsfrom one channel at a time, receive channel circuit 400 can receivesignals from a plurality of channels simultaneously or nearlysimultaneously. Moreover, receive channel circuit 400 can use many ofthe same components to perform both spectrum analysis functions andtouch sensor panel detection functions. Doing so can reduce the diespace needed to demodulate channels in different operating modes.Moreover, channels can be multiplexed, thereby using fewer mixers todemodulate multiple channels. Note that the solid-line connections inFIG. 4 a can represent receive channel circuit 400 configured as touchsensor panel detection logic, and the dashed-line connections canrepresent receive channel circuit 400 configured as spectrum analyzerlogic. FIG. 4 a will be discussed in greater detail hereinafter.

Receive channel circuit 400 will now be described when configured astouch panel detection logic. In the example illustrated in FIG. 4 a,receive channel circuit 400 can demodulate N channels (each channel isreferenced as CH[0], Ch[1] . . . CH[N−1] in FIG. 4 a). In one example,the number of channels, N, can be ten, but it is understood that thenumber of channels can be varied and is not limited to any particularnumber. Although the present disclosure typically describes receivechannel circuit 400 coupled to a plurality of channels, in accordancewith various embodiments, the number of channels, N, can be equal toone.

With further reference to FIG. 4 a, each channel can be coupled to aseparate sense line of a touch sensor panel. Analog-to-digital (ADC)blocks 402 of receive channel circuit 400 can be coupled to respectivechannels to receive raw signals from the sense lines of the touch sensorpanel and covert the signals into digital signals (also referred toherein as “digital samples”). In accordance with various embodiments,ADC block 402 can include an amplifier, such as a charge amplifier orprogrammable gain amplifier (PGA), an anti-aliasing filter and an ADC.

Delay Memory block 404 can receive and store the digital samplesoutputted from ADC blocks 402 coming from all channels at the same time.FIG. 4 a references the digital samples outputted from ADC blocks asCH[0]_ADC_out, CH[1]_ADC_out . . . CH[N−1]_ADC_out. Accordingly, ifthere is a total of ten channels being fed into receive channel circuit400, then Delay Memory block 404 can store digital samples values fromall ten channels.

From Delay Memory block 404, the digital samples can be fed into ScanMode Selector block 406. Scan Mode Selector block 406 can be configuredto switch between a spectrum analysis phase and a touch sensor paneldetection phase, wherein Scan Selector block 406 outputs the digitalsamples (CH[0]_ADC_out, CH[1]_ADC_out . . . CH[N−1]_ADC_out) to MultinSelector block 408 during the touch sensor panel detection phase. ScanMode Selector block 406 can include a scan_mode input to switch the ScanMode Selector block 406 between touch panel detection phase and spectrumanalysis phase. In accordance with various embodiments, the Scan ModeSelector block 406 can include a multiplexer or switch for example,operable to pass either the digital samples or the digital samplefrequencies depending upon its present scan mode (i.e., spectrumanalysis mode or touch panel detection mode).

Multin Selector block 408 can multiplex a plurality of sets of digitalsamples. In accordance with various embodiments, the Multin Selectorblock 408 can select a first half of digital samples (e.g., five of tendigital samples) to be sent to Multiplier block 414 at a first time anda second half of the digital samples (e.g., the remaining five of tendigital samples) to be sent to Multiplier block 414 at a second time.However, it is understood that the digital samples can be divided intomore than two sets in other embodiments.

Multin Selector block 408 can include a multiplexer and amultin_selector input for controlling which set of digital samples aresent to Multiplier block 414. The multin_selector input can receivecontrol signal 412, which can be a clock signal in accordance withvarious embodiments. In embodiments using such a clock signal, a firstset of digital samples can be sent to Multiplier block 414 on a firstedge of a clock cycle and a second set of digital samples can be sent toMultiplier block 414 at a second clock cycle edge. Accordingly, in theexample of the digital samples being divided into two sets, all of thedigital samples can be sent to multiplier block 414 during one clockcycle. In accordance with various embodiments, the clock cycle can havea frequency of 4 megahertz (MHz).

As discussed above, a plurality of sets of digital samples can be sentfrom Multin Selector block 412 to Multiplier block 414 at differenttimes. Multiplier block 414 can then mix each digital sample with awindowed demodulation waveform using a signal multiplier, for example.The demodulated output from each signal multiplier can then be stored inaccumulator 416.

In accordance with various embodiments, the number of multipliers usedin multiplier block 410 can be equal to the number of digital samples ineach set of digital samples sent by Multi Selector block 414. Thus, fivemultipliers can be used in an example of Multin Selector 408 dividing atotal of ten digital samples into two sets of five digital samples. Inthis manner, instead of needing a multiplier for each digital samplereceived from all of the channels connected to circuit 400, fewermultipliers can be used, since the number of digital samples sent toMultiplier block 414 at a particular time can be reduced by multiplexingusing Multin Selector block 408.

As discussed above, during a touch panel detection phase, each digitalsample can be demodulated by mixing the digital sample with ademodulation wave form. With further reference to FIG. 4 a, numericallycontrolled oscillator (NCO) 420 can digitally generate a demodulationwaveform synchronized to the input stimulation signal applied to thedrive lines of the touch sensor panel. In accordance with variousembodiments, the demodulation waveform can be a sine wave. In addition,NCO 420 can include a numerical control input to set an outputfrequency, a control input to set a delay, and a control input to enableNCO 420 to generate an in-phase (I) or quadrature (Q) signal or both. Inaccordance with various embodiments, NCO 420 can generate both anin-phase and quadrature signal simultaneously time.

The digital demodulation waveform generated by NCO 420 can then be mixedwith a window function generated by Amplitude Window Generator 422 usingmixer 426, resulting in a windowed digital representation of ademodulation waveform. In accordance with various embodiments, theAmplitude Window Generator 422 can include an amplitude lookup table(AmpLUT) that outputs windowed digital amplitude values over time. Theoutput of mixer 426 can then be applied to each mixer used in multiplierblock 414 so as to mix the windowed digital representation of thedemodulated waveform with the digital samples in each set of digitalsamples.

Receive channel circuitry 400 will now be described when configured asspectrum analysis logic. When receive channel circuit 400 is configureda touch panel detection logic, receive channel circuit 400 can receivedigital samples from each channel connected to respective ADC blocks402. However, when configured for spectrum analysis phase, all outputfrom ADC blocks 402 can be summed together using summing circuit 428,such as an adder circuit, into, effectively, a single digital samplerepresenting the sum of all of the digital samples (hereinafter alsoreferred to as “the summation of the digital samples”) received from thechannels. FIG. 4 a references a signal representative of summation ofthe digital samples as ΣCH[N]_ADC_out.

The output of the summation circuit 428 can then pass throughmultiplexer 424 and then be mixed with a windowing function (supplied byAmplitude window block 422) using mixer 426. The output from mixer 426(i.e. a windowed summation of the digital samples) can then be fed intoMultiplier block 414.

During spectrum analysis, the windowed summation of the digital samplescan then be separately mixed with a plurality of sample frequencies. Thesample frequencies can be generated by NCO 420, fed through Scan ModeSelector block 406 and into Multin Selector block 408. Similar to howthe digital samples can be applied to Multiplier block 414 during touchpanel detection phase, as described above, Multin Selector block 408 candivide the sample frequencies into two sets, and apply a first set ofthe sample frequencies to Multiplier block 414 at a first time and asecond set of the plurality of sample frequencies at a second time. Thewindowed summation of the digital samples (outputted from mixer 426) canthen be demodulated with each of the sample frequencies using mixers inMultiplier block 414.

In accordance with various embodiments, the timing used to apply eachset of sample frequencies to the Multiplier block 414 can be the same asis used during touch panel detecting phase; for example at each clockedge of a control signal. Moreover, the number of sample frequencies canbe the same as the number of digital samples received from the channelsof the touch sensor panel. Accordingly, in the example of using tenchannels, ten different sample frequencies can be used. Similar to themixing of the digital samples during touch panel scanning, the tensample frequencies can be divided into two sets and separately mixedwith the windowed summation of the digital samples. In this manner, allof the multipliers used during touch panel scanning can also be usedduring spectrum analysis. In accordance with various embodiments, theten digital sample frequencies can include five in-phase (I) signals andfive quadrature (Q) signals.

Accumulator 416 can then accumulate the output from Multiplier block414. The accumulated output can then be transmitted as result 440 forprocessing to identify low noise frequencies to be used during a touchpanel detection phase.

FIG. 4 b illustrates a sine look-up table (LUT) used to provide adigital values for NCO 420 to construct a sine waveforms in accordancewith various embodiments. The configuration of using sine LUT 452 withNCO 420 of FIG. 4 a can be used in receive channel circuit 400 togenerate sine waveforms. As illustrated, 16-bit counter 450 can provide14 bit values used as an address look-up into sine LUT 452. Each entryin the sine LUT 452 can be a binary representation of an angle of a sinewaveform that is represented by the 14 bit value. In accordance withvarious embodiments, the size of a sine LUT 452 can be reduced by takingadvantage of the symmetry of the sine waveform. For example, a quarterof a sine waveform can be saved in the LUT and the remaining quadrantsof the waveform can be derived based on the symmetry of the sine waveusing the remaining two bits of the 16-bit counter, where one of theremaining bits can represent a positive or negative value of thereconstructed sine wave and the second of the remaining bits canrepresent whether the absolute value of the of the sine waveform isincreasing or decreasing.

Note that various components of FIGS. 4 a-4 b can be implementeddigitally instead of in analog circuitry inside an ASIC. Havingcomponents implemented digitally instead of in analog circuitry insidethe ASIC can save a significant amount of die space and further reducepower consumption.

FIG. 5 a illustrates exemplary timing diagram 500 showing LCD phase 502and the vertical blanking or touch sensor panel phase 504 according tovarious embodiments. During LCD phase 502, the LCD can be activelyswitching and can be generating voltages needed to generate images. Nopanel scanning need be performed at this time. During touch sensor panelphase 504, the receive circuit 500 can be configured as a spectrumanalyzer to identify low noise frequencies, and can also be configuredas touch panel detection logic to detect and locate an image of touch.

It should be noted that the touch sensor phase 504 need not be limitedto being performed before or after the LCD phase 502. For example, inone embodiment, the touch sensor phase is performed during the LCDphase. By performing the touch sensor phase 504 during the LCD phase502, a spectrum analysis can take into account any noise generatedduring the LCD phase 502. Moreover, in one embodiment, there is notiming association between the LCD phase 502 and the touch sensor 504.In other words, the sensor phase 504 need not be synchronized with LCDphase 502.

FIG. 5 b illustrates exemplary flow diagram describing process 501performing LCD phase 502 and touch sensor panel phase 504 according tovarious embodiments. In Step 0, the LCD can be updated as describedabove. The various tasks performed in connection with process 501 may beperformed by hardware, software, firmware, or any combination thereof.It should be appreciated that process 501 may include any number ofadditional or alternative tasks. The tasks shown in FIG. 5 b need not beperformed in the illustrated order and process 501 may be incorporatedinto a more comprehensive procedure or process having additionalfunctionality not described in detail herein. For illustrative purposes,the following description of process 501 may refer to elements mentionedabove in connection with FIGS. 1-4.

Steps 1-3 can represent a low noise frequency identification phase 506.In Step 1, receive channel circuit 400 can be configured as a spectrumanalyzer. The purpose of the spectrum analyzer is to identify severallow noise frequencies for subsequent use in a panel scan. With nostimulation frequencies applied to any of the drive lines of the touchsensor panel, the sum of the output of all ADC blocks 402, whichrepresent the total charge being applied to the touch sensor panelincluding all detected noise, can be windowed and fed into Multiplierblock 414. Multiplier block 414 can demodulate the sum of all ADCchannel output using the in-phase (I) and quadrature (Q) signals ofselect frequencies. The demodulated outputs can be used to calculate themagnitude of the noise at that particular frequency, wherein the lowerthe magnitude, the lower the noise at that frequency.

In Step 2, the process of Step 1 can be repeated for a different set offrequencies. In accordance with various embodiments, Step 2 need not beperformed if the number of frequencies used in Step 1 is sufficient forthe desired application. Furthermore, in accordance with otherembodiments, Step 1 can be performed more than two times, each time withdifferent sets of frequencies.

In Step 3, one or more low noise frequencies can be selected for use ina subsequent touch sensor panel scan by identifying those frequenciesproducing the lowest calculated magnitude value.

Step 4 can represent a panel scan phase 508. In Step 4, the receivechannel circuit 400 can be configured as panel scan logic. At Step 4,various phases of the one or more selected low noise frequencies can beused to simultaneously stimulate the drive lines of the touch sensorpanel, and the Multiplier block 414 can be configured to demodulate thesignals received from each sense line using the selected low noisefrequencies. The demodulated signals from the multiplier block 414 canthen be saved.

In Step 5, after all steps have been completed, the saved results can beused in calculations to determine an image of touch for the touch sensorpanel at each of the selected low noise frequencies.

Referring again to the example as shown in FIG. 4 a, while receivechannel circuit 400 is configured as a spectrum analyzer, no stimulationsignal need be applied to any of the drive lines in the touch sensorpanel. In the present example, there can be 10 channels and therefore 10ADC blocks 402, one mixer for every two channels in Multiplier block 414(i.e. 5 mixers), and one mixer 426 used to mix a window function, for atotal of 6 mixers. The outputs of all ADC blocks 402 in receive channelcircuit 400 can be summed together using summing circuit 428, and fedinto Multiplier block 414 through multiplexer or switch 424, which canbe configured to select the output of summing circuit 428 instead of NCO420.

While receive channel circuit 400 is configured as a spectrum analyzer,the background coupling onto the sense lines can be measured. Because noVstim is applied to any drive line, there is no Csig at any pixel, andany touches on the panel should not affect the noise result (unless thetouching finger or other object couples noise onto ground). By addingall outputs of all ADC blocks 402 together in summing circuit 428, onedigital bitstream can be obtained representing the total noise beingreceived into the touch sensor panel. The frequencies of the noise andthe pixels at which the noise is being generated are not known prior tospectrum analysis, but do become known after spectrum analysis has beencompleted. The pixel at which the noise is being generated is not knownand is not recovered after spectrum analysis, but because the bitstreamis being used as a general noise collector, they need not be known.

While configured as a spectrum analyzer, the mixers in Multiplier block414, in the present example of FIG. 4 a, can be used to demodulate I andQ signals for different frequencies as generated by NCO 420. Thesefrequencies can be between 200 kHz and 300 kHz, for example. NCO 420 canproduce a digital rampsine wave that can be used by the digital mixersin Multiplier block 414 to demodulate a windowed noise output of summingcircuit 428.

The output of summing circuit 428 (the noise signal) can then bedemodulated by I and Q components of the frequencies using digitalmixers in Multiplier block 414. The result of each mixer can beaccumulated in separate accumulators in accumulator block 416. Eachaccumulator can be a digital register that, over a sample time period,can accumulate (add together) the instantaneous values from the mixers.At the end of the sample time period, the accumulated value canrepresent an amount of noise signal at that frequency and phase.

The accumulated results of I and Q demodulation at a particularfrequency can represent the amount of content at that frequency that iseither in phase or in quadrature. These two values can then be used inmagnitude and phase calculation circuit (not shown) to find the absolutevalue of the total magnitude (amplitude) at that frequency. A highermagnitude can mean a higher background noise level at that frequency.The magnitude value computed by each magnitude and phase calculationcircuit can be saved. Note that without the Q component, noise that wasout of phase with the demodulation frequency can remain undetected.

This entire process can be repeated for different frequencies, ifdesired. The saved magnitude values for each of the frequencies can thenbe compared, and one or more frequencies with the lowest magnitudevalues (and therefore the lowest noise levels), can be chosen.

Still referring to FIG. 4 a, when receive channel circuit 400 isconfigured as touch panel detection logic, the dashed lines in FIG. 4 acan be ignored. At Step 4 in FIG. 5 b, various phases of the selectedlow noise frequencies can be used to simultaneously stimulate the drivelines of the touch sensor panel, and the receive channel circuit 400 canbe configured to demodulate the signal received from each sense lineconnected to the receive channel circuit 400 using a selected low noisefrequency. The demodulated signals from each digital signal mixer inMultiplier block 414 can then be accumulated in accumulator block 416,and saved.

It can be noted that Step 4 of FIG. 5 b can combine two features,multi-phase scanning and multi-frequency scanning. Each feature can haveits own benefit. In some embodiments, multi-frequency scanning can savetime by a factor of three, while multi-phase scanning can provide abetter signal-to-noise ratio (SNR) by about a factor of two.

Multi-phase scanning can be employed by simultaneously stimulating mostor all of the drive lines using different phases of multiplefrequencies. Multi-phase scanning is described in Applicant's co-pendingU.S. application Ser. No. 11/619,433 entitled “Simultaneous SensingArrangement,” filed on Jan. 3, 2007, the contents of which areincorporated by reference herein. One benefit of multi-phase scanning isthat more information can be obtained from a single panel scan.Multi-phase scanning can achieve a more accurate result because itminimizes the possibility of inaccuracies that can be produced due tocertain alignments of the phases of the stimulation frequency and noise.

In addition, multi-frequency scanning can be employed by simultaneouslystimulating most or all of the drive lines using multiple frequencies.As noted above, multi-frequency scanning can save time. For example, insome previous methods, 15 drive lines can be scanned in 15 steps atfrequency A, then the 15 drive lines can be scanned in 15 steps atfrequency B, then the 15 drive lines can be scanned in 15 steps atfrequency C, for a total of 45 steps. However, using multi-frequencyscanning, fewer steps can be performed.

At the conclusion of Step 4, when the results have been obtained andstored, additional calculations can be performed utilizing theseresults. For example, for each channel M, where M=0 to N, computationscan be performed to obtain a drive line result for each drive line andeach frequency used to stimulate the drive lines. A set of computationsfor each channel can generate a resultant pixel value for the sense lineof pixels associated with that channel. For example, a Drive Line 0,frequency A computation (xa1[chM]+xa2[chM]+xa3[chM]+xa4[chM])/4 cangenerate the Drive Line 0, channel M result for frequency A. Computationcan be performed and stored for every channel. These computationscorrespond to Step 5 of FIG. 5 b.

The results for a particular frequency can represent an image map orimage of touch at that frequency because a unique value is provided foreach sense line (i.e. channel) and drive line intersection. These touchimages can then be processed by software that synthesizes the threeimages and looks at their characteristics to determine which frequenciesare inherently noisy and which frequencies are inherently clean. Furtherprocessing can then be performed. For example, if three frequencies areused to stimulate the drive lines and all three are relativelynoise-free, the results of each three frequencies can be averagedtogether.

FIG. 6 a illustrates an exemplary mobile telephone 636 that can includetouch sensor panel 624, display device 630 bonded to the sensor panelusing pressure sensitive adhesive (PSA) 634, and other computing systemblocks in computing system 100 of FIG. 1 for applying multiplestimulation frequencies and phases to the touch sensor panel to identifylow noise stimulation frequencies and detect and localize touch eventsusing receive channel circuit 400 according to various embodiments ofthe invention.

FIG. 6 b illustrates an exemplary digital audio/video player 640 thatcan include touch sensor panel 624, display device 630 bonded to thesensor panel using pressure sensitive adhesive (PSA) 634, and othercomputing system blocks in computing system 100 of FIG. 1 for applyingmultiple stimulation frequencies and phases to the touch sensor panel toidentify low noise stimulation frequencies and detect and localize touchevents using receive channel circuit 400 according to variousembodiments of the invention.

Note that one or more of the functions described herein can be performedby firmware stored in memory (e.g. one of the peripherals 104 in FIG. 1)and executed by panel processor 102, or stored in program storage 132and executed by host processor 128. The firmware can also be storedand/or transported within any computer-readable medium for use by or inconnection with an instruction execution system, apparatus, or device,such as a computer-based system, processor-containing system, or othersystem that can fetch the instructions from the instruction executionsystem, apparatus, or device and execute the instructions. In thecontext of this document, a “computer-readable medium” can be any mediumthat can contain or store the program for use by or in connection withthe instruction execution system, apparatus, or device. The computerreadable medium can include, but is not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus or device, a portable computer diskette (magnetic), a randomaccess memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), anerasable programmable read-only memory (EPROM) (magnetic), a portableoptical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flashmemory such as compact flash cards, secured digital cards, USB memorydevices, memory sticks, and the like.

The firmware can also be propagated within any transport medium for useby or in connection with an instruction execution system, apparatus, ordevice, such as a computer-based system, processor-containing system, orother system that can fetch the instructions from the instructionexecution system, apparatus, or device and execute the instructions. Inthe context of this document, a “transport medium” can be any mediumthat can communicate, propagate or transport the program for use by orin connection with the instruction execution system, apparatus, ordevice. The transport readable medium can include, but is not limitedto, an electronic, magnetic, optical, electromagnetic or infrared wiredor wireless propagation medium.

Although embodiments of this invention have been fully described withreference to the accompanying drawings, it is to be noted that variouschanges and modifications will become apparent to those skilled in theart. Such changes and modifications are to be understood as beingincluded within the scope of embodiments of this invention as defined bythe appended claims.

What is claimed is:
 1. A method of scanning a touch sensor panel, thetouch sensor panel comprising a plurality of drive lines and a pluralityof sense lines, the method comprising: a first mode for identifying oneor more scanning frequencies corresponding to low noise, the first modecomprising: deactivating one or more of the plurality of drive lines;sensing a first plurality of outputs from the plurality of sense lines;demodulating the sensed first plurality of outputs using a firstplurality of mixers with a demodulation frequency; summing the firstplurality of outputs; comparing the summation at the demodulationfrequency to one or more other summation values at other frequencies;and determining the one or more scanning frequencies of the touch sensorpanel based on the comparison.
 2. The method of claim 1, furthercomprising: a second mode for scanning the touch sensor panel, thesecond mode comprising: stimulating the drive lines at the one or morescanning frequencies; sensing a second plurality of outputs from theplurality of sense lines; demodulating the sensed second plurality ofoutputs using a second plurality of mixers; and forming a touch imageusing the sensed second plurality of outputs.
 3. The method of claim 2,wherein the drive lines are stimulated at multiple scanning frequencies.4. The method of claim 2, wherein the touch image is formed by averagingthe sensed second plurality of outputs at multiple scanning frequencies.5. The method of claim 2, wherein a number of scanning frequencies isequal to a number of second plurality of mixers.
 6. The method of claim2, wherein the second plurality of mixers is the same as the firstplurality of mixers.
 7. The method of claim 2, wherein the touch sensorpanel is operating the first mode is at a same time as the second mode.8. The method of claim 1, further comprising: generating thedemodulation frequency using a numerically controlled oscillator (NCO).9. The method of claim 1, wherein demodulating the sensed firstplurality of outputs includes at least one of an in-phase and quadraturesignals of the demodulation frequency.
 10. The method of claim 1,wherein the plurality of sense lines are divided into a number of sets,the number of sets equal to the number of ones in the first plurality ofmixers.
 11. The method of claim 1, wherein at least one of the one ormore scanning frequencies is the same as the demodulation frequency. 12.The method of claim 1, wherein the first mode further comprises: storingthe summation at the demodulation frequency in a register.
 13. Themethod of claim 12, wherein comparing the summation at the demodulationfrequency to one or more other summation values at other frequenciescomprises selecting a frequency with a summation value less than each ofthe one or more other stored summation values at the other frequencies.14. The method of claim 1, the method further comprising: generating oneor more voltages on a display included in the touch sensor panel duringa same time as sensing the first plurality of outputs.
 15. An apparatusfor obtaining a plurality of values used to generate an image of touchfrom a touch sensor panel comprising: a circuit configured to deactivateone or more of a plurality of drive lines of the touch sensor panel; asense circuit configured to sense a plurality of outputs from aplurality of sense lines of the touch sensor panel; a plurality ofmixers configured to mix the sensed plurality of outputs with ademodulation frequency; a summation circuit operable to generate a sumrepresentative of a summation of the plurality of outputs; a comparatorto compare the sum generated by the summation circuit at thedemodulation frequency to one or more other sums at other frequencies;and a processor configured to identify one or more low noise frequenciesbased on the compared results.
 16. A computing system comprising theapparatus of claim
 15. 17. A mobile telephone comprising the apparatusof claim
 15. 18. A digital audio player comprising the apparatus ofclaim 15.